2 
GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
For the purposes of tliis Guide, it is more couvenieut to 
take the collections iu the reverse order from that given 
above, namely, to begin with Gallery XI. The description 
of the specimens exhibited iu that Gallery serves to explain 
the meaning of fossils and the use made of them iu inter- 
preting the structure and history of the earth. We then 
proceed to Galleries X, VIII, and VII, beginning with the 
simplest forms of life and passing gradually to those more 
highly organised. Under each group of animals too, the 
description generally begins with the older fossils and traces 
the history of the group down to our own day. In order to 
follow this method of description, it is, iu Galleries X and 
VIII, necessary to visit the Cases in the reverse order of 
their numbering. 
The collections in Galleries X, VIII, and VII are 
arranged, in the main, according to a zoological classification, 
the specimens bedonging to the various large groups of the 
Animal Kingdom being placed together. In some gi’oups it 
has been found more convenient to subdivide the specimens 
according to the geological epochs to which they belong, and 
under each of those epochs again to arrange them in zoological 
order. In other groups the zoological system is the dominant 
one throughout, all species of each genus being placed 
together. It is also the general nile that the specimens 
from British localities are exhibited in the Table-cases, and 
those from foreign localities iu the Wall-cases. This, how- 
ever, is not rigidly adhered to ; for example, among the 
larger specimens mounted on blocks and placed usually 
towards the back of the Wall-cases may often be found 
several British specimens, whicli have to be exhibited there 
on account of then- size. 
Although all the animals whose fossil remains are herein 
described are often spoken of collectively as luvertebrata, or 
backbone-less animals, in contrast to the Vertebrata, or 
animals with a backbone, yet it must be remembered that 
this common usage does not represent a scientific classifica- 
tion. It is nearer the truth to say that each of the larger 
groups named above — Mollusca, Arthropoda, Echiuoderma, 
Coelentera, and the rest — has the same independence and 
importance as a division of the Animal Kingdom as has the 
whole group of Vertebrata. Just as the Vertebrata are 
divided into Classes, namely. Mammals, Birds, Keptiles, 
Amphibians, and Fishes, so is each of these great groups, or 
Phyla as they are termed, divided into Classes. Each Class 
